High-activity supported Ziegler-Natta catalysts are widely used in olefin polymerization. A conventional process for preparing such high-activity supported catalysts is co-precipitating process, wherein a magnesium halide is dissolved in a solvent system to form a homogeneous solution, which is then treated with titanium halide to precipitate active magnesium halide, and at the same time and/or thereafter, active titanium component is supported on the active magnesium halide. U.S. Pat. No. 4,784,983 discloses a catalyst system for olefin (co)polymerization comprising (a) a titanium-containing solid catalyst component, (b) an alkyl aluminum compound, and (c) an organic silicon compound. The (a) component is obtained by dissolving a magnesium halide in a solvent mixture consisting of an organic epoxy compound and an organic phosphorus compound to form a homogeneous solution; mixing the solution with a titanium tetrahalide or its derivatives; precipitating a solid in the presence of an auxiliary precipitant selected from the group consisting of carboxylic acid anhydrides, carboxylic acids, ethers and ketones; treating the solid with a polycarboxylic acid ester to support the polycarboxylic acid ester onto the solid; and treating separated solid with titanium tetrahalide or a mixture of titanium tetrahalide and an inert diluent. When used in propylene polymerization, the catalyst exhibits high activity, and the resultant polymer has a high isotacticity and a high bulk density.
Patent Application CN1229092 discloses a process for preparing a catalyst similar to that of U.S. Pat. No. 4,784,983, wherein in the step of dissolving magnesium halide to form a homogeneous solution, ethanol is added to modify the magnesium halide. Such prepared catalyst exhibits greatly enhanced activity when used in ethylene polymerization, however, said catalyst is not applicable to the production of polypropylene and copolymer of ethylene and propylene.